The Flavonoids

The Flavonoids Edited by

J. B. HARBORNE Reader In Phytochemlstry University of Reading, U.K.

T. J. MABRY Professor

and HELGA MABRY

Research Assistant,

Department of Botany University of Texas at Austin, U.S.A.

Springer-Science+Business Media, B.Y.

© Springer Science+Business Media Dordrecht Originally published by Chapman and Hall Ltd in 1975. Softcover reprint ofthe hardcover 1st edition 1975

ISBN 978-0-12-324602-8 ISBN 978-1-4899-2909-9 (eBook) DOI 10.1007/978-1-4899-2909-9

All rights reserved. No part of this book may be reprinted, or reproduced or utilized in any form or by any electronic, mechanical or other means, now known or hereafter invented, including photocopying and recording, or in any information storage and retrieval system, without permission in writing from the Publisher.

Library ofCongress Catalog Card Number 74-12868

Contents

page

Contributors vii

Preface x Introduction XlI

T. A. Geissman

1. Isolation techniques for flavonoids 1 Ken R. Markharn

2. Ultraviolet-visible and proton magnetic resonance 45 spectroscopy of tlavonoids

Ken R. Markharn and Tom J. Mabry

3. Mass spectrometry of flavonoids 78 Tom J. Mabry and Ken R. Markharn

4. Synthesis of flavonoids 127 Hildebert Wagner and Lorand Farkas

5. Anthocyanins 214 C. F. Timberlake and P. Bridle

6. Flavones 267 K. Venkataraman

7. Flavonols 296 Otto Richard Gottlieb

8. Flavone and flavonol glycosides 376 Jeffrey B. Harborne and Christine A. Williams

9. Cha1cones, aurones and dihydrocha1cones 442 Bruce A. Bohm

10. Natural proanthocyanidins 505 E. Haslam

11. Flavanones and dihydroflavonols 560 Bruce A. Bohm

v

vi CONTENTS

12. C-Glycosylflavonoids 632 J. Chopin and M. L. Bouillant

13. Biflavonoids 692 Hans Geiger and Christopher Quinn

14. Isoflavonoids 743 E. Wong

15. Neoflavanoids 801 Dervilla M. X. Donnelly

16. Biosynthesis of flavonoids 866 Klaus Hahlbrock and Hans Grisebach

17. Metabolism of flavonoids 916 Wolfgang Barz and Wolfgang Hösel

18. Physiology and functions of flavonoids 970 Jerry W. McClure

19. Biochemical systematics of flavonoids 1056 J. B. Harborne

20. Evolution of flavonoid compounds 1096 T. Swain

Addenda 1130

Author Index 1139

Plant Species Index 1177

Subject Index 1197

W. BARZ

B. A. BOHM

M. L. BOUILLANT

P. BRIDLE

J. CHOPIN

Contributors

Lehrstuhl für Biochemie der Pflanzen, Westfälische-Wilhelms­Universität, 44 Münster/Westf. Hindenburgplatz 55, Germany

Department of Botany, Univer­sity of British Columbia, Van­couver, Canada

Laboratory of Biological Chemis­try, University of Lyon, 69 Villeurbanne, France

Long Ashton Research Station, University of Bristol, U.K.

Laboratory of Biological Chemis­try, University of Lyon, 69 Villeurbanne, France

DERVILLA M. X:. DONNELLY Chemistry Department, Univer­sity College, Belfield, Dublin 4, Ireland

L. FARKAS

H. GEIGER

T. A. GEISSMAN

Institut für Pharmazeutische Arzeimittelehre, 8-München-2, Karlstrasse 29, Germany

Fachgruppe 1, Universität Hohenheim, D-7000-Stuttgart-70, Windhalmweg 14, Germany

Department of Chemistry, University of California, Los Angeles, U.S.A.

vii

viii

O. R. GOTTLlEB

H. GRISEBACH

H. HAHLBROCK

J. B. HARBORNE

E. HASLAM

W. HÖSEL

T. J. MABRY

K. R. MARKHAM

1. McCLURE

C. QUINN

T. SWAIN

C. F. TIMBERLAKE

CONTRIBUTORS

Instituto de Quimica, Univer­sidade de Sao Paulo, Brazil

Biologisches Institut 11 der Universität, Schänzlestr. 9-11, D-7800 Freiburg/Br., Germany

Biologisches Institut 11 der Universität, Schänzlestr. 9-11, D-7800 Freiburg/Br., Germany

Plant Sciences Laboratories, The University, Reading, U.K.

Department of Chemistry, The University, Sheffield, U.K.

Lehrstuhl für Biochemie der Pflanzen, Westfälische-Wilhelms­Universität, 44 Münster/Westf., Hindenburgplatz 55, Germany

The Cell Research Institute and Department of Botany, Univer­sity of Texas at Austin, Texas 78712, U.S.A.

Chemistry Division, D.S.I.R., Petone, New Zealand

Department of Botany, Miami University, Oxford, Ohio, U.S.A.

School of Botany, University of New South Wales, Kensington, NSW 2033, Australia

Biochemical Laboratory, Royal Botanic Gardens, Kew, Surrey, U.K.

Long Ashton Research Station, University of Bristol, Bristol, U.K.

CONTRIBUTORS ix

K. VENKATARAMAN

H. WAGNER

CHRISTINE A. WILLIAMS

E. WONG

National Chemical Laboratory, Poona 8, India

Institut für Pharmazeutische Arzeimittelhre, 8-München-2, Kar1strasse 29, Germany

Plant Sciences Laboratories, The University, Reading, U.K.

Applied Biochemistry Division, D.S.I.R., Palmerston North, New Zealand

Preface

The flavonoids, one of the most numerous and widespread groups of natural constituents, are important to man not only because they contribute to plant colour but also because many members (e.g. coumestrol, phloridzin, rotenone) are physiologically active. Nearly two thousand substances have been described and as a group they are universally distributed among vascular plants. Although the anthocyanins have an undisputed function as plant pigments, the raison d'etre for the more widely distributed colourless flavones and flavonols still remains a mystery. It is perhaps the challenge of discovering these yet undisc10sed functions which has caused the considerable resurgence of interest in flavonoids during the last decade.

This book attempts to summarize progress that has been made in the study of these constituents since the first comprehensive monograph on the chemistry of the flavonoid compounds was published, under the editorship of T. A. Geissman, in 1962. The present volume is divided into three parts. The first section (Chapters 1-4) deals with advances in chemistry, the main emphasis being on spectral techniques to take into account the re cent successful applications of NMR and mass spectral measurements to structural identifications. Recent developments in isolation techniques and in synthesis are also covered in this section. Advances in chemical knowledge of individual c1asses of flavonoid are mentioned inter aha in later chapters of the book.

The main section of the volume (Chapters 5-15) is concemed with providing a comprehensive account of the known structural variation among the fifteen c1asses of flavonoid compound. The need for a modem listing of all the known flavonoids has become more and more acute since so many new substances have been reported in re cent years. Although the various contributors in this section have interpreted their tasks in different ways, this part of the book should

PREFACE

provide, at least for the next deeade, an indispensable guide to the ehemieal structures of flavonoid compounds.

One of the major changes of emphasis in the flavonoid field sinee 1962 has been away from purely chemical aspects towards bio­chemistry, systematic distribution and biological funetion. The last section (Chapters 16-20) therefore contains a summary of some of the more significant developments in these disciplines. Ten years ago, practically not hing was known of the enzymology of flavonoid biosynthesis; now, as is dear from Chapter 16, most of the enzymes involved have been detected and some of them have been fully charaeterised. Again, it is only recently that the turnover and metabolie fate of flavonoids have been seriously investigated and the results of the very latest experiments are induded in Chapter 17. The final three essays eover more biological aspects and review what is known of the physiology, function, systematics and evolution of flavonoids.

The editors are grateful to their contributors, who have responded valiantly and courteously to all the demands made on them. They are particularly grateful to Professor T. A. Geissman for contributing the introduction. Finally, they thank the publishers for their guidance and assistance.

December 1974 Reading, U.K. and Austin, U.S.A. The Editors.

Introduction

T. A. GEISSMAN

A little more than ten years have passed since the appearance of the first comprehensive account of the chemistry of flavonoid com­pounds. During that time a number of books, monographs and reviews, dealing with overall ar selected aspects of the subject have appeared, all of which have contributed to what may be regarded as a recrudescence which has led to so substantial an enlargement of knowledge as to warrant the present volume.

In common with studies of naturally occurring compounds of all kinds, flavonoid chemistry has emerged from the undirected search for new compounds, and the establishment of their structures by conventional means, and has been increasingly directed into areas of inquiry in which biological considerations come to play an increas­ingly important role. Nevertheless, it is still apparent that methods of isolation and separation and efficient procedures for structure analysis are essential to rapid progress in the field, and to these ends many advances have been made in fundamental methodology. The most useful of these have been the development of rapid and effective means of separation of mixtures derived from plant materials, and the application of modern instrumental techniques far the study of structure.

The improvement in chromatographie methodology far separa­tions and identifications has increased the ease with which complex mixtures can be separated and their components recognized or isolated. Applications of chromatographie procedures have often been used for the scanning of large numbers of plants of related varieties, species and genera as a means of examining chemosystem­atic relationships; and the re cent burgeoning of interest in this aspect of flavonoid (and other) chemistry can be ascribed in part to the availability of improved techniques and in part to a growing

INTRODUCTION

recognition of chemosystematics as an important area of inquiry. Although paper chromatography has not been entirely superseded, the use of column and thin-Iayer analytical and preparative chro­matography has greatly increased the flexibility of these techniques. Spectroscopic methods - in particular, in the ultraviolet and visible regions - have been used for many years in the analysis of flavonoid structures; and refinements of these procedures and recent develop­ments in the use of proton magnetic resonance and optical properties, have made it increasingly practicable to deal with very small amounts of material for the complete determination of structure and stereochemistry.

Establishment and confirmation of the structures of flavonoid compounds by total synthesis has continued to develop, and to the fundamental early approaches developed by Robinson, Seshadri, Venkataraman, Zemplen and others have been added many recent contributions. A variety of ingenious manipulations of functional groups have provided convenient procedures for the synthesis of flavonoid compounds with a wide range of functional substitution patterns, and have made possible the synthesis of flavonoid com­pounds with comparative ease.

The upshot of these several developments, many of them accomplished in recent years, is that it is now possible to assay the complex constitution of plant materials with relative ease and certainty, and in terms of the complete structures of the individual constituents. The importance of this facility to considerations of biological aspects of flavonoid chemistry cannot be overemphasized. It is to be anticipated that flavonoid chemistry will find its most interesting future developments in areas c10ser to biology than to the c1assical areas of structural organic chemistry, and considerations of biological origins and biological function must rest upon accurate structural information, and upon a thorough knowledge of constitu­ents that co-occur in nature.

Significant progress has been made within the past decade in the solution of problems relating to the biological origins and inter­relationships of flavonoid compounds. The fundamental processes leading to the generation of the common precursors, inc1uding the discovery of specific enzyme systems involved; the understanding of the manner in which alkylations and glycosylations are accom­plished, again with respect to enzymes and prosthetic units; and the

INTRODUCTION

developing techniques of synthesis in cell-free systems pro mise soon to reveal complete synthetic sequences from simple precursors to complex end products.

Among recent developments have been the discovery and ex­panded study of a number of flavonoid compounds of novel types. The class of neo-flavonoids has been enlarged by the discovery of new structural variants which can be accommodated into rational hypotheses of biosynthetic relationships. The formation of the biflavonyls provides additional examples of the phenol oxidative coupling process, counterparts of which are found in many classes of natural phenolic compounds. The study of the dimeric and oligo­meric compounds that constitute the flavonoid tannins, or the related leucoanthocyanidins, has been brought to a stage at which these ubiquitous compounds and their structures are understood, although some details remain to be provided. Aurones and chalcones, once a restricted group of flavonoid compounds of limited botanical distribution, have been found in many new sourees. Carbon-linked glycosides (C-glycosides), of which vitexin and its structural isomer were for many years the only known representatives, are now recognized as constituents of many plant groups, and are known in a large number of structural variations.

Many questions remain to be answered, and it seems likely that progress during the coming decade will equal or surpass that of the one past. An area in which much of interest remains to be discovered is that of the biological function and physiological properties of flavonoid compounds. Their formation as a result of injury and invasion of infective agents, their role as phytoalexins, and their possible participation in primary metabolie processes raise questions to which answers are only beginning to appear.

This book will, by providing an up-to-date summary of the state of knowledge in the field, serve as a new starting point for the investigations of the coming decade, after which, no doubt, another will have to be written.